Fixation screw and method for ligament reconstruction

ABSTRACT

A screw for fixation of a tendon/bone graft during an arthroscopic surgical procedure includes a smooth conical forward end having a rounded tip and a spiral thread running from a position behind the smooth rounded forward end to a rearward end of the screw. The depth of the thread is shallower than a conventional screw and the exterior edge of the thread is rounded to decrease cutting and fragmentation of the tendon and bone. The screw includes an internal bore with left- and right-handed threaded portions for engagement with insertion and extraction instruments. In the method, the bone graft is harvested and sized as desired. A graft socket is drilled in the bone and then serially sized with increasingly larger sizing instruments to compact the bone and size the graft socket to the graft. A smooth bore screw socket is created by serially dilating a space between the graft and graft socket with increasingly larger dilating instruments, thereby also compacting the graft. The appropriately sized fixation screw is then inserted into the screw socket with the insertion instrument to fix the graft to the bone.

This is a continuation of application Ser. No. 08/111/970, filed on Aug.26, 1993, now abandoned, which is a continuation of Ser. No. 07/848,546,filed on Mar. 9, 1992, now abandoned, which is a divisional of Ser. No.07/721,893, filed Jun. 27, 1991, now U.S. Pat. No. 5,116,337, issued onMay 26, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a screw for fixation of a bone/tendongraft during a surgical procedure and particularly, to arthroscopicanterior cruciate ligament reconstruction.

2. Related Art

Ligament reconstruction by replacing the ligament with a tendon/bonegraft is well known in the art. For instance, during arthroscopic kneesurgery, a surgeon can form a tunnel through the tibia, intra articularjoint and femur to receive a bone-tendon-bone graft harvested from thepatellar tendon. A variety of techniques have been employed to securethe bone-tendon-bone graft, such as tying sutures over ligament buttons,staples, unicortical screw posts, or interference screws. An example ofone such ligament anchor system is disclosed in U.S. Pat. No. 4,870,957,which is incorporated by reference herein.

One common example of interference screw is the self-tapping Kurosakascrew which cuts its own threads into the bone and graft. With this typeof screw, the graft bone plug is sized to be smaller than the receptivebone tunnel to provide clearance for the screw to begin self-tapping andthreading. However, there are many disadvantages to such types ofscrews. Since there is no preformed channel for the screw to enter, butrather, the screw cuts its own channel within the clearance between thebone and the graft, the screw can diverge, reducing screw thread to boneplug contact. The self-tapping operation cuts into the graft, therebypossibly causing graft damage or fragmentation. The insertion of thescrew can also cause migration or translocation of the graft.

Further, the Kurosaka type screw is not well secured to the insertiondevice and can fall off the insertion device as well as require a K-wireinsertion. The bone tunnel is usually created with an acorn type drillhead which can cause cavitation of the tunnel wall and the depth of thetunnel is not controlled.

SUMMARY OF THE INVENTION

The preferred exemplary embodiment of the present invention includes ascrew for fixation of a tendon/bone graft to a bone. Thenon-selftapping, non-thread cutting screw includes a smooth conicalforward end having a rounded tip. A right-handed spiral thread runs froma position behind the smooth rounded forward end to a rearward end ofthe screw. The depth of the thread is shallower than conventionalinterference screws and the thread has a rounded exterior edge todecrease cutting and fragmentation of the tendon and bone.

The screw includes an internal longitudinal bore with a right-handedthreaded portion and a left-handed threaded portion having a smallerdiameter than the right-handed threaded portion. An insertion devicewith a right-handed threaded portion can be engaged with theright-handed threaded portion of the screw bore to screw the screw intoa prepared screw socket. A left-handed threaded extraction device can beengaged with the left-handed portion of the internal bore to extract thescrew. The screw can be fixed by inserting a wire in a radial boredisposed in a rearward portion of the screw for removal of the insertionor extraction devices without disturbing the placement of the screw.

In the method for fixation of the tendon/bone graft, a bone-tendon-bonegraft is harvested from the patellar tendon. Each bone plug of thebone-tendon-bone graft is harvested in a semicircular cross-section witha semicircular gouge and is conventionally sized. A graft socket is thendrilled into the bone with an anti-cavitational drill. The bonesurrounding the drilled socket is compacted by sizing the socket with aseries of increasingly larger tubular sizing instruments until thecompacted socket is sized to accomodate the bone plug.

The bone plug is then inserted into the compacted socket and positionedas desired. The bone plug may be held in place by a conventional K-wireor with sutures, if necessary. The bone plug is compacted into thecompacted socket by inserting a series of increasingly larger tubulardilating instruments between the compacted socket and the bone plug,thereby forming a screw socket. After the largest dilating instrumenthas been used, the compacting of the socket and bone plug can becontinued with the larger sizing instruments as discussed above. Whenthe next larger size sizing instrument cannot be manually inserted intothe screw socket, the screw size is chosen to be the same as the size ofthe compacted screw socket, i.e., the same size as the last dilating orsizing instrument that could be inserted into the screw socket.

The sized screw is then screwed onto the insertion tool, whereupon thescrew is threaded into the screw socket, thereby securing the bone plugto the bone. If necessary, an extraction tool can be screwed into theleft-handed threaded portion of the internal bore to extract the screw,either slightly or entirely. The same method is also carried out withthe other bone plug of the bone-tendon-bone graft, with the method stepsfor fixing the two bone plugs overlapping. The remainder of the surgicaloperation proceeds conventionally.

Thus, the screw of the present invention enters a precreated unthreaded,smooth wall screw socket of compressed bone, thereby creating a maximumtight fit for the screw threads and a side-to-side compression fitbetween the bone plug and bone. The precreated screw socket preventsdivergence of the screw and migration of the graft. Only the initialsocket is drilled and threads are not cut into the bone or bone plug,thereby preventing cutting and fragmentation of the bone plug. Rather,the screw fixes the bone plug through the use of displacement andcompression. The screw need not be made of expensive alloys but can beconstructed of surgical stainless steel.

With the foregoing in mind, other objects, features and advantages ofthe present invention will become more apparent upon consideration ofthe following description and the appended claims with reference to theaccompanying drawings, all of which form part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the fixation screw of the presentinvention;

FIG. 2 is a rear elevational of the fixation screw;

FIG. 3 is a sectional view taken along section line 3--3 of FIG. 2;

FIG. 4 is a side elevational view of a patient's knee showing thefixation screws of the present invention fixing a bone-tendon-bonegraft;

FIG. 5 is an end elevational view of the semicircular harvested boneplug;

FIG. 6 is a side elevational view of a sizing instrument;

FIG. 7 is a side elevational view of a dilating instrument; and

FIG. 8 is a schematic diagram illustrating the steps for preparing bonefor receiving a medical device or biological material by sizing a borein bone and compacting the internal wall of the bore in accordance withthe present invention; and

FIG. 9 schematically illustrates the results of preparing bone forreceiving a medical device or biological material in accordance withprior art methods and in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT

FIGS. 1-3 show a preferred embodiment of a fixation screw 10 accordingto the present invention. The screw has a smooth conical forward end 12with a rounded tip 14 and is of a headless design. A right-handed spiralthread 16 runs from a position behind the smooth conical forward end 14to a rearward end 18 of the screw 10. The depth of the thread 16 isshallower than conventional interference screws and the thread 16 has arounded exterior edge 20 and root to decrease cutting and fragmentationof the bone.

The screw includes an internal longitudinal bore 22 with a right-handedthreaded portion 24 and a smaller diameter left-handed threaded portion26 nearer the forward end 12. A right-handed threaded insertion device(not shown) can be engaged with the right-handed threaded portion 24 forscrewing the fixation screw 10 into a prepared screw socket. Aleft-handed threaded insertion device (not shown) can be engaged withthe left-handed threaded portion 26 for extraction of the screw 10. Ofcourse, in an alternative embodiment, spiral thread 16 and threadedportion 24 can be left-handed while threaded portion 26 is right-handed.

The screw 10 further includes a radial bore 28 located near the rearwardend 18. A wire (not shown) can be placed in the bore 28 to preventrotation of the screw 10 while the insertion or extraction device isbeing removed from the screw 10. In the preferred embodiment, the screw10 is made from surgical stainless steel and need not be made from anexpensive alloy. Of course, other appropriate materials can also be usedas well known in the art, including biodegradable material.

In the preferred embodiment, the screw 10 is 25 to 40 mm long and has 5threads/inch, regardless of the outer diameter of the screw 10, whichcan be 5, 7, 9, 11 or 13 mm. The exterior edge 20 and root 21 arerounded to a 0.02 inch radius and the height of the thread 16 from root21 to exterior edge 20 is 0.065 inch. The thread 16 does not extenddiametrically beyond the largest outer diameter of the conical forwardend 12. The forward end 12 has an angle of 28 degrees from alongitudinal axis of the screw to the exterior conical surface of theforward end 12. Threaded portion 24 has an 8-32 right-handed thread andthreaded portion 26 has a 6-32 left-handed thread.

In the method for fixation of the tendon/bone graft, for instance, inarthroscopic reconstruction of the anterior cruciate ligament, abone-tendon-bone graft is harvested from the patellar tendon, asconventionally known. Each bone plug 30 of the bone-tendon-bone graft isharvested in a semicircular cross-section, as shown in FIG. 5, with asemicircular gouge. Reference can also be made to FIG. 4 which shows thebone-tendon-bone graft 40 secured in a patient's knee 42 with thefixation screws 10. The size of the bone-tendon-bone graft ispredetermined for each individual patient and in the preferredembodiments, a 9, 10 or 11 mm (and 12 & 13 mm) diameter semicircularbone plug 30 is harvested on each end of the bone-tendon-bone graft.Each bone plug is then conventionally shaped and sized to the desireddimensions.

Next, a blind graft socket 44 is drilled in the femur 46 with ananti-cavitational drill, which is provided in 8, 9, 10 and 11 mmdiameters. The anti-cavitational drill does not have an acorn-type headthat can drill out-of-round holes or cavitate the graft socket, therebydeteriorating the bone plug to graft socket fit. Rather, the drill hasstraight sides with a rounded tip. A through socket can also be drilledif desired or for a different application. The size of the drill ischosen to be smaller than the size of the bone plug 30. For instance, ifthe bone plug 30 is 11 mm, an 8 mm graft socket is initially drilled.

The bone surrounding the graft socket 44 is then compacted and the graftsocket 44 enlarged and sized by manually inserting a sizing instrument32 having a larger diameter than the selected drill into the graftsocket 44. The sizing instrument 32 is shown in FIG. 6 and is tubularwith a blunt forward end 34 having rounded edges. The sizing instrument32 can also have a conical or other shape forward end in an alternativeembodiment.

The sizing of the graft socket 44 is preferably done serially withincreasingly larger sizing instruments 32 until the graft socket 44 hasbeen sized to the size of the bone plug 30 and the surrounding bone hasbeen firmly compacted. During the sizing of the socket 44, no bone isintended to be removed, but instead the bone is outwardly displacedwithin the cavity, thereby compacting the bone surrounding the socket44. This provides denser and stronger bone surrounding the socket whichis able to withstand higher stress than the uncompacted bone. If thegraft socket 44 cannot be sized large enough for the harvested bone plug30, preferably the graft socket 44 would be redrilled with a largerdrill and then resized, if necessary, as discussed above. This willdepend on the hardness of the bone and the degree of compaction of thebone that can achieved. Alternatively, the bone plug 30 can be resizedto be smaller to fit the sized graft socket 44.

The sized bone plug 30 of the bone-tendon-bone graft is then insertedinto the sized graft socket 44 to the bottom of the graft socket 44 andpositioned as desired. The placement of the bone-tendon-bone graft 40can be eased with the use of a standard guide wire inserted into thegraft. If necessary, the bone plug can be held in place by aconventional K-wire or with sutures. The bone plug 30 is compacted intothe graft socket 44 with a smooth tubular dilating instrument 36 havinga conical forward end 38, as shown in FIG. 7. In an alternativeembodiment, the forward end 38 can be more blunt or more rounded or haveanother shape.

The dilating instrument is provided in 4, 5, 6, 7 and 8 mm sizes and isinserted into the cavity between the semicircular bone plug 30 and thegraft socket 44 to compact the bone plug 30, further compact the graftsocket 44 and to size a screw socket for receiving the fixation screw10. As with the sizing of the graft socket 44, the compacting of thebone plug is done serially with increasingly larger diameter dilatinginstruments 36 and sizing instruments 32 until the desired diameterscrew socket is achieved or until the next larger dilating instrument 36or sizing instrument 34 cannot be manually inserted into the screwsocket. Preferably, the screw socket is sized to be smaller in diameterthan the sized bone plug 30. For instance, if a 10 mm bone plug is used,the screw socket would only be sized to 8 mm, for use with an 8 mmdiameter screw 10. A screw having a larger diameter than the screwsocket can also be used, if even further compaction of the graft socketand bone plug is desired.

The screw 10 is then screwed onto the insertion device for insertioninto the screw socket. The screw 10 is screwed into the screw socketuntil it bottoms, then is turned an additional small amount to makecertain that everything is secure. If a blind graft socket was not used,then the screw 10 is screwed in until it reaches a desired position. Theinsertion device can then be removed from the screw 10. If necessary, awire can be temporarily inserted into the radial bore 28 to secure thescrew 10 while the insertion device is being removed. If extraction ofthe screw 10 is necessary, the extraction device can now be used.

The same method is used for the second bone plug 30 of thebone-tendon-bone graft 40, with the method steps for fixing the two boneplugs 30 overlapping. Any undiscussed portions of the surgical operationproceed conventionally. After 4 to 6 weeks there will be a bony unionbetween the bone plugs and the femur and tibia, respectively, and thefixation screws will no longer have any function. The screws will notgenerally be removed at this time, although they can be.

The method for preparing bone which has been described above isschematically illustrated in FIG. 8, and a comparison of the results ofsuch preparation and those obtained by known methods is shown in FIG. 9.More particularly, FIG. 8 illustrates a cylindrical bore having adiameter d₀ into which dilating and compacting instruments havingincreasing larger diameters, d₁ -d₃, are successively inserted toincrease the diameter of the bore and compact the bone surrounding thewall of the bore. The results of such compaction are indicated in FIG. 9wherein the bone density of the bore's wall is shown to be significantlygreater than that obtainable by merely forming the bore to the correctsize in accordance with known techniques.

Although the procedure discussed above is in reference to reconstructionof the anterior cruciate ligament, it should be realized that the screwand method of the present invention can be used in other ligament/tendonreconstructive applications, arthroscopic or otherwise. Further, thesizes and shapes of the drills, screws, sizing instruments and dilatinginstruments can also be altered as necessary. The screws 10 and drillscan be cannulated for use with a guide wire, as conventionally known.

The method of preparing the bone for receiving the screw can also beused in many other surgical operations.

While the invention has been described in accordance with what ispresently conceived to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andthe scope of the appended claims, which scope is to be accorded thebroadest interpretation of such claims so as to encompass all suchequivalent structures.

What is claimed is:
 1. A method for fixation of a tendon/bone graft to abone, comprising the steps of:sizing one end of the tendon/bone graft tothe desired size; drilling a graft socket in the bone; compacting thebone surrounding the graft socket by sizing the socket with at least onesizing instrument having a diameter greater than a diameter of thedrilled socket; inserting the sized end of the tendon/bone graft intothe sized graft socket; compacting the bone of the tendon/bone graftinto the graft socket with at least one dilating instrument, therebyforming a sized screw socket; inserting a fixation screw into the sizedscrew socket.
 2. A method as in claim 1, wherein the drilling is donewith an anti-cavitational drill.
 3. A method as in claim 1, wherein thebone compacting step is done with a series of increasingly largerdiameter sizing instruments.
 4. A method as in claim 1, wherein thetendon/bone graft compacting step is done with a series of increasinglylarger diameter dilating instruments.
 5. A method as in claim 1, whereinthe tendon/bone graft compacting step further includes compacting withat least one sizing instrument having a diameter larger than the lastused dilating instrument.
 6. A method as in claim 5, wherein the sizinginstrument compacting step is done with a series of increasingly largerdiameter sizing instruments.
 7. A method as in claim 1, wherein thescrew is inserted with an insertion device that threads into a firstthreaded portion of an internal bore in the screw in a direction ofrotation of an external thread of the screw.
 8. A method as in claim 1,wherein the inserted screw may be extracted with an extraction devicethat threads into a threaded portion of an internal bore in the screw ina reverse direction of rotation of an external thread of the screw.
 9. Amethod as in claim 1, and further comprising the step of inserting afixation wire into a radial bore in a rearward portion of the insertedscrew to fix the screw while at least one of an insertion device and anextraction device is being removed from the screw.
 10. A method ofpreparing bone for receiving a medical implant, comprising the stepsof:creating an initial bore having a side wall in the bone; compactingthe bone along the side wall without intentionally removing bone byinserting within the bore a first sizing instrument having a diametergreater than the diameter of the initial bore; and further compactingthe previously compacted bone along the side wall without intentionallyremoving bone by increasingly enlarging the bore by sequentiallyinserting within the bore at least two additional sizing instrumentshaving different diameters, each greater than the diameter of the firstsizing instrument, and having portions inserted within the bore whichhave a common geometry.
 11. A method as in claim 10, wherein the initialbore is created by drilling.
 12. A method as in claim 11, wherein thedrilling is done with an anti-cavitational drill.
 13. A method as inclaim 10, wherein the initial bore is created by inserting a rotatableinstrument into the bone.
 14. A method as in claim 13, wherein therotatable instrument creates the bore by displacing and compacting bonewithout removing bone.
 15. A method of preparing bone for receiving amedical implant, comprising the steps of:creating an initial cavityhaving a side wall in the bone; compacting the bone on the side wall ofthe cavity without intentionally removing bone by inserting within thecavity a first sizing instrument having a cross-sectional area greaterthan a cross-sectional area of the initial cavity; and furthercompacting the previously compacted bone on the side wall withoutintentionally removing bone by increasingly enlarging the cavity bysequentially inserting within the cavity at least two additional sizinginstruments having different cross-sectional areas, each greater thanthe cross-sectional area of the first sizing instrument, and havingportions inserted within the cavity which have a common geometry.